Ok, I've come up with an untested theory that a resistive absorber will give better low end performance if the space behind is a sealed cavity as opposed to say a panel spaced from the wall.
My reasoning is that having the space sealed creates an active cavity resovoir to modulat the sound pressure intake and release, almost a physical version of a capacitor that can smooth out electrical signals by means of storage. I think this is the operating principle behing 'tube traps'
Is there any studies on this out there or anyone who has tesed this?
I've tried simulations in water and it seems to work well.
Sealed cavity bass trap.
Originally posted at johnlsayers.com, topic 8751.
But have you done the comparison against how much lost absorbtion due to the back side being exposed in a spaced off situation?
This is a hotly debated topic - especially in corner mounted situations.
Bryan
Bryan. No I haven't compared the two. I don't quite understand what you mean. I don't see how there would be a loss of absorption by sealing it off, maybe I wasn't clear.
Ok imagine a 2" 2' by 4" piece of 703 or whatever attached to a wall and spaced out say 4" with the gap behind the panel completely open VS the same panel 4" from wall but with a frame around the perimeter that attaches to the wall forming a box with the wall with the 703 becoming one side of the box.
My theory is that having an entrance with high impedence and a lower impedence cavity behind will in essence allow the air pressure to enter but not escape rapidly.
Or maybe I misunderstood you?
I don't recall this topic in debate before, any links?
Start with Rose's acoustics paper (http://www.bbc.co.uk/rd/pubs/archive/pdffiles/architectural-acoustics/bbc_guideacousticpractice.pdf) and the earlier absober papers from the BBBC RD archives. There is at least one abosrber desigb that uses that general design (space behind absorbent material) and has various test results.
Andre
"having an entrance with high impedence and a lower impedence cavity behind will in essence allow the air pressure to enter but not escape rapidly"
Sounds like part of the patent language for a Helmholtz... Steve
Yeah I suppose, just with a different operating principle, The entrance being resistive instead of sized to determine resonance. Maybe there is something to this 8)
I wish I had more time to be able to build a couple of them for tests.